Tooth root canal posts, screws or anchors have existed in dentistry since ca 1750. These items are inserted in the tooth root canal and serve as retention or anchorage for a re-building of the ruined tooth crown, which had to be done, using a plastic material.
To avoid the need for the dentist to build up the core in plastic material, posts with fixed crown cores, in addition to the ordinary posts, were introduced in the early 1900, so Davis posts, ca 1920 and Kurer crown posts ca 1970. They all consist of a large cylinder or head part to serve as crown core and a post or anchor part attached to the bottom of the crown part, the anchor part to be inserted in the root canal.
All these posts show a disadvantage in that there is a point of breakage in the junction between the head and the much narrower root part. There is also no possibility to regulate the length of the root post except cutting it off at the end, thereby with the danger of cutting off special features provided at the point of this part. It is also known that threaded dowels have tendency to fracture and also tight fitting dowels have tendency to exert lateral forces when it is cemented.
Another aspect of root canal treatments is that there is a need to give access to the root canal for preparation and reconstruction before closing definitively the root canal with a post. To this end, inserts or sleeves are fixed in the tooth, having a bore with a greater diameter than the root canal. After the last treatment, a post is inserted into the bore of the sleeve. This sleeve can also serve to fix a rubber dam.
EP-A2-0 245 878 and EP-A1-0 113 792 disclose a tooth root canal anchorage assembly according to the introduction of claim 1 of the present invention, wherein a sleeve as core member with a through bore is cemented into a corresponding hole extending around the root canal. A post, having also a through bore is inserted in the sleeve and fixed into the root canal. The sleeves disclosed are cylindrical, with a collar and the posts are conventional ones with a conical anchoring part. The disclosed shape of the sleeves call for drilling a cylindrical bore with a relatively large diameter, leading to weaken the tooth.